(a) Field of the Invention
A curtain blinds spring motor elasticity maintaining structure, for use with a window curtain blind set that applies a horizontal taking-in and letting-down operation that is provided with a self-contained feedback function for taking up the curtain blinds. The structure primarily consists of a spring motor structure that prevents unproductive deformation and loss of elastic stress in a sheet band of a coil spring.
(b) Description of the Prior Art
Referring to FIG. 1, which shows a window curtain blind set 100 provided with an elastic self-contained feedback function to take up curtain blinds 15, which is basically installed with a spring motor 10 provided with an elastic feedback function. Two sides of the spring motor 10 respectively connectively drive curtain pull cords 14 to achieve a taking-up and letting-down operation of the curtain pull cords 14. Accordingly, the curtain blinds 15 are let down when the curtain pull cords 14 are let down, and when a self-contained feedback take-up operation is performed, the curtain pull cords 14 are taken up, which connectively drives the complete taking up of the curtain blinds 15. The spring motor 10 comprises a coil spring 4, which uses coiling of the coil spring 4 under the pulling of an external force to let down the curtain blinds 15, and at the same time reversely stored elastic deformation energy back feeds the actuation of two side spools 13, and corresponding ends of the curtain pull cords 14 are wound onto the respective wheel faces of the two side spools 13 to completely take up the curtain blinds 15.
Referring to FIG. 2, which shows the spring motor 10 installed with a take-up drum 2 and an idler gear 5, wherein the take-up drum 2 has no rotational speed relationship with the idler gear 5, and the take-up drum 2 and the idler gear 5 are in a coaxial relationship. The spring motor 10 is further installed with a linkage gear 30 that connects with the idler gear 5 through parallel-axes meshing. The linkage gear 30 integrally connectively drives a drive drum 3, enabling front and rear connection between the take-up drum 2 and the drive drum 3 through the coil spring 4. When there is no external force being applied, the coil spring 4 forms a reset coil 41 that is coiled round the outer circumference of the take-up drum 2, while another end of the coil spring 4 connectively drives the outer circumference of the drive drum 3. When the spools 13 are actuated by pulling on the curtain pull cords 14, the spools 13 further respectively connectively drive driven gears 131 with shafts 130 respectively serving as centers of rotation. The driven gear 131 meshes with the linkage gear 30, and the linkage gear 30 further coaxial connects to the drive drum 3, whereupon a sheet band 400 is pulled and wound onto the outer circumferential surface of the drive drum 3, at which time deformation of the sheet band 400 is used to produce elastic accumulation energy. Furthermore, the idler gear 5 is in a separation rotary motion relationship with the take-up drum 2, but the idler gear 5 meshes with the linkage gear 30. Another end of the idler gear 5 further meshes with the right side driven gear 131, and the driven gear 131 forms a single body with the spool 13, thereby enabling synchronous rotation through the support of the right side shaft 130. Hence, the surface of the spool 13 enables winding-unwinding of the right side curtain pull cord 14 thereon.
Referring to FIG. 3 (together with FIG. 2), which shows connection of the sheet band 400 to the reset coil 41. After pulling the curtain pull cords 14, one end of the drive drum 3 forms a pressure accumulating coil 42, and under the effect of an external force, the coil spring 4 restores the reset coil 41.
Referring further to FIG. 4, which shows the drive drum 3 and the linkage gear 30 in a coaxially interconnected relationship, with the take-up drum 2 and the idler gear 5 in a separation rotary motion relationship. When there is no external force burden being imposed on the sheet band 400 of the coil spring 4, the sheet band 400 is wound up according to the outer circumferential surface of the take-up drum 2 to form the reset coil 41, and the reset coil 41 forms a convex drum shape, the reason for which is that the body of the sheet band 400 itself uses the cross-sectional curvature to produce elastic stress, and changes in the cross-sectional curvature of the sheet band 400 form an elastic reaction force. The installed drive drum 3 is a round shaft shaped cylindrical body of uniform radius in common use. Hence, as shown in FIG. 2, the sheet band 400 is actuated by the curtain pull cords 14, which pulls and winds the sheet band 400 onto the outer circumferential surface of the drive drum 3 to form a pressure accumulating coil 42. A first wound layer 421, a second wound layer 422, a third wound layer 423 . . . of the pressure accumulating coil 42 are sequentially overlapped onto the outer circumference of the drive drum 3.
Because the outer circumference of the drive drum 3 is a cylindrical form of uniform radius, and the surface thereof is a round flat surface, thus, the pressure accumulating coil 42 formed after winding the sheet band 400 onto the drive drum 3, the inner and outer windings of each of the wound layers including the first wound layer 421, the second wound layer 422, the third wound layer 423 . . . are sequentially pressed flat by a pulling force. In particular, the cross-sectional curvature of the inner winding of the first wound layer 421 will be flattened.
Referring to FIG. 5, which shows changes in the aforementioned flattening. The drive drum 3 is a round cylindrical shaft form of uniform radius, and the sheet band 400 is wound thereon in wound layers to form the pressure accumulating coil 42, wherein the first wound layer 421, the second wound layer 422, and the third wound layer 423 are pulled by two side pulling forces F2 and F3, subjecting the center of the band body of the sheet band 400 to the flat surface center point of contact of the drive drum 3 therewith, which produces a reverse pressing force F1. Hence, the pressure accumulating coil 42 wound round and formed on the drive drum 3 with a flat round surface, similar to that shown in FIG. 4, forms flat overlapping layers. The flat overlapping layers then force changes in the degree of curvature of the arched cross section of the sheet band 400 to occur. If the changes occur within a short period of time, then recovery is immediate, and the elastic stress will not have a large affect on the cross-sectional curvature of the sheet band 400. However, in general, curtains are continuously in a let-down mode for over 10 hours during the day, which causes the pressing force F1 and the pulling forces F2 and F3 to accumulate pressure over a long period of time that produces pressure deformation in the cross-sectional curvature of the sheet band 400, thereby causing changes in the cross-sectional curvature of the sheet band 400 and loss in elastic stress, and is thus unable to maintain its appropriate elastic recovery capacity.